Many herbicides injure crop plants at herbicide application rates necessary to control weed growth. Accordingly, many herbicides cannot be used for controlling weeds in the presence of certain crops. Uncontrolled weed growth, however, results in lower crop yield and reduced crop quality inasmuch as weeds compete with crops for light, water and soil nutrients. Reduction of herbicidal injury to crops without an unacceptable corresponding reduction of herbicidal action on the weeds can be accomplished by use of crop protect ants known as herbicide "antidotes" or "safeners".
Certain substituted-aryl cyclopropanecarbonitrile compounds and derivatives are known. For example, the compound 1-naphthyl-1-cyclopropanecarbonitrile is shown in a publication of Makosza et al [Rocz. Chem., 49, 297 (1975)], but without mention of any specific biological activity for this compound. U.S. Pat. No. 4,399,076 describes 1,1-disubstituted 2-vinyl/2-ethyl cyclopropanes as herbicides. Belgian Patent No. 900,594 describes certain halophenylcyclopropanecarbonitrile compounds, namely, 1-(2-fluorophenyl)cyclopropanecarbonitrile, 1-(4-fluorophenyl)cyclopropanecarbonitrile and 1-(4-chlorophenyl)cyclopropanecarbonitrile, as intermediates for preparation of triazoleethanol compounds used as fungicides. EPO Patent No. 94,085 describes the compound 4-chlorophenylcyclopropanecarboxylic acid as an intermediate for preparation of 1-(4-chlorophenyl)cyclopropanemethanol for use as an insecticide. Belgian Patent No. 902,147 describes 1-(4-ethoxyphenyl)cyclopropanecarbonitrile as an intermediate for preparation of compounds useful as pesticides. A publication of D. D. Roberts et al mentions the compound 1-(4-nitrophenyl)cyclopropanecarboxylic acid for use in determination of cholsteryl tosylate solvolysis rates [J. Org. Chem., 35 (4), 978-81 (1970)].
None of the foregoing patents or publications mentions any use of the described compounds as antidotes for herbicides.
An effective herbicide must provide a relatively high level of control of grassy or broad leaf weeds, or both, in the presence of crops in addition to meeting several other criteria. For example, the herbicide should possess relatively high unit activity so that lower rates of herbicide application are feasible. Lower application rates are desirable in order to minimize exposure of the environment to the herbicide. At the same time, such herbicide must be selective in herbicidal effect so as not to injure the crops. Herbicidal selectivity can be enhanced by use of an appropriate antidote in combination with the herbicide. But identification of an antidote which safens a herbicide in crops is a highly complicated task. Whether a compound or class of compounds provides efficacious antidote or safening activity is not a theoretical determination but must be done empirically. Safening activity is determined empirically by observing the complex interaction of several biological and chemical factors, namely: the type of herbicide compound; the type of weed to be controlled; the type of crop to be protected from weed competition and herbicidal injury; and the antidote compound itself. Moreover, the herbicide and antidote must each possess chemical and physical properties enabling preparation of a stable formulation which is environmentally safe and easy to apply to the field.